Biomedical subjects

David Assif

Publications and source records attributed to David Assif.

4 recordsLinked to original sources

PubMed2006

Heat transfer of impression plasters to an implant-bone interface.

PURPOSE: The purpose of this in vitro study was to measure heat generated at the implant-bone interface caused by exothermic setting reaction of 2 impression plasters. MATERIALS AND METHODS: The study consisted of 20 titanium-alloy abutment impressions connected to a titanium-alloy cylindrical implant embedded in an acrylic-resin mandible in a 37 degrees C water bath. There were 2 types of impression plaster used, Snow-White (Kerr, Romulus, MI) and Xantano (Kulzer, Dormagen, Germany). Temperature changes were recorded via embedded thermocouples at the cervix and implant surface apex. Analysis of variance for repeated measures was used to compare 2 treatment groups. RESULTS: Temperature increased less at the implant apex (1.5 degrees-2.1 degrees C) than at the implant cervix (7.4 degrees-10.5 degrees C). Differences between the 2 impression plasters were statisticallysignificant only at the implant cervical level (P < 0.05). A lower temperature increase was shown with the Snow-White compared with the Xantano. Although both plasters generated an exothermic reaction on setting (mean temperature change 22 degrees C), the increase in the temperature rate of the Snow-White was slower than the Xantano. CONCLUSIONS: Under the conditions of the present study, Snow-White impression plaster appears to be safer to use in implant prosthodontics compared with the Xantano because of its slower and lower exothermic reaction at the implant-bone interface. However, use of the material with the rapid setting time would require more care, such as limiting the volume of material used (e.g., by using a custom tray).

Acrylic Resins↗

PubMed2003

Assessment of the resistance to fracture of endodontically treated molars restored with amalgam.

STATEMENT OF PROBLEM: Controversy exists concerning the preferred type of final restoration of endodontically treated molars regarding their resistance to fracture under occlusal load. PURPOSE: The aim of this study was to assess the resistance to fracture of endodontically treated molars with various degrees of tooth structure loss restored with amalgam under simulated occlusal load. MATERIAL AND METHODS: . The study teeth consisted of 90 noncarious, nonrestored molars stored in physiological saline solution. The teeth were endodontically treated and randomly divided into 9 experimental groups of 10 specimens each with various degrees of tooth loss, ranging from a conservative endodontic access to removal of all cusps. All teeth were restored with a standardized technique to their original contour with amalgam. Each specimen was mounted onto a specialized jig for loading at the central fossa at a 30-degree angle to the long tooth axis. The resistance to fracture, under continuous compressive force at a cross-head speed of 2 mm/minute, was applied by a universal testing machine and was recorded. One-way analysis of variance with Scheffé contrast was used to statistically compare the differences between the groups at significance level P<.05. RESULTS: One-way analysis of variance showed that the group with a conservative endodontic access (1137.6 +/- 311.6 N) and the group with removal of all cusps (1261.4 +/- 195.1 N) presented a significantly higher resistance to fracture when compared with the other groups (P<.05). There was no significant difference in resistance to fracture under the simulated load between the other 7 groups, which ranged from 655.8 +/- 229.4 to 906.3 +/- 168.1 N (P>.05). CONCLUSION: Within the limitations of this study, the endodontically treated molars with a conservative endodontic access or after removal of all cusps that were restored to their original contour with amalgam presented the highest resistance to fracture under a simulated occlusal load.

Analysis of Variance↗

PubMed2002

Effect of core stiffness on the in vitro fracture of crowned, endodontically treated teeth.

STATEMENT OF PROBLEM: Dentin and core materials that substitute for missing dentin are dissimilar materials. A core material with a lower elastic modulus may deform more under applied stress and therefore result in reduced stress concentration at the core/dentin junction. PURPOSE: This in vitro study examined the effect of core stiffness on the fracture resistance and failure characteristics of a crowned, endodontically treated tooth under simulated occlusal load. MATERIAL AND METHODS: Forty extracted human mandibular premolars were divided equally into 4 groups and prepared for posts and cast crowns as follows: group 1 = cast post and core, cast crown; group 2 = preformed metal post, composite core, and cast crown; group 3 = preformed metal post, amalgam core, and cast crown; and group 4 (control) = preformed metal post, no core, and cast crown. All prepared teeth had 2 mm of sound dentin on which the cemented crown rested. A continuous load (kg) was applied to the buccal cusp at a 30-degree angle to the long axis of each tooth at a crosshead speed of 2 mm/min until failure. Collected data were subjected to 1-way analysis of variance with the Welch modification to compare groups (P<.05). RESULTS: Failure loads for the 4 test groups were as follows: 98.1 +/- 34.6 kg (group 1), 94.4 +/- 41.8 kg (group 2), 105.5 +/- 18.6 kg (group 3), and 101.1 +/- 55.3 kg (group 4). No significant difference in failure load values was found among the 4 groups. The primary mode of failure (80%) in all groups was an oblique radicular fracture, either apical to the post or at the post level. Horizontal fracture of the root and post was found in groups 1, 2, and 3 (20%). Loosening of the crown, post, and core was found only in group 2(20%). CONCLUSION: Within the limitations of this study, core stiffness did not affect the failure resistance of teeth restored with posts and cores and complete-coverage cast metal crowns. The dominant pattern of failure was unrepairable root fracture. Only the composite core exhibited repairable fractures.

Bicuspid↗

PubMed2002

Impression technique for partially edentulous patients.

This article describes an implant impression technique for partially edentulous patients in which impression plaster and irreversible hydrocolloid are used. The technique ensures accuracy, ease of manipulation, and decreased working time.

Alginates↗